What is a CTF?
A CTF is a game designed to let you learn to hack in a safe, rewarding environment. CTF contests are usually designed to serve as an educational exercise to give participants experience in securing a machine, as well as conducting and reacting to the sort of attacks found in the real world
The CTF challenges contestants to solve a variety of tasks ranging from a scavenger hunt on wikipedia to basic programming exercises, to hacking your way into a server to steal data. In these challenges, the contestant is usually asked to find a specific piece of text that may be hidden on the server or behind a webpage. This goal is called the flag, hence the name!